In continuous phase modulations, the information is carried by the phase. These modulations are interesting for their spectral effectiveness, their spectral power and their constant amplitude. Therefore, these modulations may be used with power amplifiers which operate near to their saturation zone.
An example of continuous phase modulation (CPM for short) is described in the document: "Reduced State Sequence Detection of Partial Response Continuous Phase Modulation", A. SWENSSON, IEE Proceedings-1, vol. 138, no. 4, 1991, pages 256 to 268. This document relates to the processing of the signals performed at the receiving end. The receiving means comprise a detector which performs a coherent detection of the baseband signal, followed by a Viterbi decoder. Such a detection does not create intersymbol interference at the receiving end. The Viterbi decoder is only provided and used for correcting the imperfections generated at the transmitting end. But such a system shows various drawbacks. First, the coherent detection needs the presence at the receiving end of a very precise oscillator, which complicates and thus increases the cost of the hardware. Moreover, the precision attained by the coherent detection is insufficient for certain applications. This is the case, for example, for low-rate transmissions (several Mbits/s, for example), for example for satellite links and for high-frequency transmissions (several GHz, for example). When the frequency/rate ratio becomes higher than, for example, 10.sup.4, the techniques described in above document become insufficient.